Domain Walls and Their Experimental Signatures ins+isSuperconductors

Abstract

Arguments were recently advanced that hole-doped Ba1−xKxFe2As2 exhibits s+is state at certain doping. Spontaneous breaking of time reversal symmetry in s + is state, dictates that it possess domain wall excitations. Here, we discuss what are the experimentally detectable signatures of domain walls in s+is state. We find that in this state the domain walls can have dipole-like magnetic signature (in contrast to the uniform magnetic signature of domain walls p + ip superconductors).We propose experiments where quench-induced domain walls can be stabilized by geometric barriers and be observed via their magnetic signature or their influence on the magnetization process, thereby providing an experimental tool to confirm s + is state.The recently discovered iron-based superconductors [1] may exhibit new physics originating in the possible frustration of inter-band couplings between more than two superconducting components [2][3][4][5]. For a two-band superconductor, inter-band Josephson interaction either locks or anti-locks phases, so that the ground state interband phase difference is respectively 0 or π. Similarly, for more than two bands, each inter-band coupling favours (anti-)locking of the two corresponding phases. However, these Josephson terms can collectively compete so that optimal phases are neither locked nor anti-locked. There, the resulting frustrated phase differences are neither 0 nor π. Since it is not invariant under complex conjugation, such a ground state spontaneously breaks the TimeReversal Symmetry (TRS) [2,3]. This is the s + is state, with the spontaneously Broken Time-Reversal Symmetry (BTRS), that recently received strong theoretical support in connection with hole-doped Ba 1−x K x Fe 2 As 2 , [5]. There are also other scenarios for BTRS states in pnictides [6,7], and related multi-component states may possibly exist in other classes of materials [8].Symmetrywise, these BTRS states break the U(1) × Z 2 symmetry. The topological defects associated with the breakdown of a discrete Z 2 symmetry are domain walls (DW) segregating regions of different broken states [9]. Other superconductors with BTRS and having domain walls are the chiral p-wave superconductors. There are evidences for such superconductivity in Sr 2 RuO 4 [10]. For that material, it is predicted that domain walls have magnetic signature and thus can be detected by measuring the magnetic field (see e.g. [11,12]). These signatures were searched for in surface probes measurements, but were not experimentally detected [13]. This led to intense theoretical investigation of possible mechanisms for the field suppression (see e.g. [14]). The problem of interaction of vortices and domain walls in these systems and magnetization process was studied in [15,16]. Domain walls between BTRS states is also highly important in rotational response of 3 He [17]. Aspects of topological defects of s + is states received attention only recently [18][19][20][21]. The remaining question is how domain walls can be created and observed in s + is superco...

s+is superconductivity with incipient bands: Doping dependence and STM signatures

“…The time-reversal symmetry-breaking in the s + is state is most directly manifested in spontaneous currents around nonmagnetic impurities 58 or quench-induced domain walls 59 . The currents result in local magnetic fields in the superconducting phase and provide a signature of the s+is state.…”

Orbital and Pauli limiting effects in heavily dopedBa0.05K0.95Fe2As2

“…The discovery of the '122' family of iron-based superconductors 2 has provided an example of unconventional superconductivity with a non-universal gap structure [3][4][5][6][7][8] .…”

High temperature effects on compact-like structures

“…[4][5][6][7][8][9][10][11][12]. Among them, the simplest topological structures are kinks, which appear in models described by real scalar fields in (1, 1) spacetime dimensions.…”